The goal of the proposed research is to examine the behavior of the resistance and the capacitance blood vessels of different vascular beds in response to stimulation of mechanoreceptors and chemoreceptors located within the high pressure and low pressure parts of the vascular system. The areas of particular interest are the receptors in the atria and great veins, the receptors in the lungs and the chemoreceptors of the carotid body. In general the approach will be to examine the response to graded excitation of a selected receptor group while eliminating the influence of other receptor groups either by maintaining them in a steady state of activity, reversible blockade of their afferent nerves, or surgical denervation. The patterns of response to excitation of a selected receptor group and of the manner in which this is affected by activation of other receptor groups will be studied by construction and comparison of stimulus response curves. Excitation of receptors will be effected through control of their natural mode of stimulation. The vascular regions to be examined will include skeletal muscle, skin, kidney and splanchnic region. It is hoped that these studies will define the pattern of sympathetic efferent activity for a given receptor group, whether this is the same or different for different receptor groups and to establish the pattern of interactions of different receptor groups in the maintenance of systemic blood pressure. During exercise there is an increase in sympathetic adrenergic activity. The extent to which afferent impulses originating from receptors in the active muscles contribute to this increase in sympathetic activity will be studied, and the degree to which the blood flow to the working muscles is modified by the exercise engendered sympathetic activity will be assessed. Bibliographic references: Shepherd, J.T.: Life Sciences. In: Scientific Uses of the Space Shuttle. Space Science Board National Research Council. National Academy of Sciences, 1974, Chapter 8, pp. 154-178. Clement, D.L. and Shepherd, J.T.: Influence of muscle afferents on cutaneous and muscle vessels in the dog. Circulation Research 35(2) 177-183, August 1974.